The present invention relates to a automotive headlamp in which a discharge lamp is used as a light source.
As shown in FIG. 1, a conventional discharge lamp 1 has a rod-like structure in which a pair of pinch seal portions 1b and 1c are formed at front and rear portions, respectively, of a glass bulb 1a, and lead wires 2 (2a, 2b), which are connected to respective ones of the opposite electrodes in the closed glass bulb 1a, extend from the end portions of the pinch seal portions 1b and 1c, respectively. The lead wires 2 (2a, 2b) are fixedly welded to respective metal supports 5 (5a, 5b), which are in turn fixedly welded to respective ones of a pair of long and short lead supports 4 (4a, 4b) projecting forward from a lamp base 3 to thereby constitute a discharge lamp device in which the discharge lamp 1 is supported at its opposite ends.
Since a discharge lamp device has an excellent luminous efficiency and output light color characteristics, discharge lamps have been seriously considered for use as a bulb for an automotive headlamp. However, the light emission of a discharge lamp includes ultraviolet rays in a wavelength range which is harmful both to health and to various constituent parts of the headlamp. It is therefore necessary to eliminate ultraviolet rays in harmful wavelength ranges.
As shown in FIG. 1 of the drawings, to block such ultraviolet rays, conventionally an ultraviolet-ray shielding globe 6 enclosing the discharge lamp 1 has been fixed to the base so as to be integrated with the discharge lamp device.
In the case where such a discharge lamp is used as a bulb of a projection-type headlamp in which light reflected from a reflector 7 is projected and distributed by a projection lens 8 as shown in FIG. 1, the greater part of the light emitted by the discharge portion (the closed glass bulb) 1a of the discharge lamp (which is positioned at a first focus position of the reflector 7) is reflected from the reflector 7, as indicated by arrows in FIG. 4, and the reflected light is radiated and distributed forward by the projection lens 8 through a second focus on a light axis to thereby form a predetermined light distribution pattern.
However, there is a problem in the resulting light distribution in that a part of the light reflected from the reflector 7, and particularly the light l.sub.1 reflected from a light reflection surface range 7a on the circumference of a bulb insertion hole, is rejected (i.e., reflected, absorbed, deflected, etc.) at a top end portion of the ultraviolet-ray shielding globe 6 (reference numeral 6a designates a portion at which the light L.sub.1 is rejected), so that the intensity of illumination of a light-distribution pattern central portion is decreased. If the length of the discharge lamp 1 is reduced (i.e., if the respective lengths of the pinch seal portions 1b and 1c are reduced), the globe 6 can be shortened longitudinally, so that the problem of the light reflected from the reflector being rejected by the globe can be overcome. However, reducing the length of the discharge lamp 1 is difficult in view of problems of sealing the lead wires, preventing leakage of the gas sealed in the closed glass bulb, etc.
Accordingly, the inventors have conducted studies as to the shape of the ultraviolet-ray shielding globe to obtain an ultraviolet-ray shielding globe which does not interfere with the light reflected from the reflector.